PHYS 255b-004 Lab - Wheatstone Bridge

PHYS 255b-004 Lab - Wheatstone Bridge - Wheatstone Bridge...

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Shannon Berg Partners: Chris and Ryan Physics 255-004 October 7, 2010 Object The object of this lab was to use the Wheatstone bridge setup to measure electrical resistance in a resistor and use this to determine an unknown resistance. Apparatus 1) Wheatstone bridge (one unknown resistor, three known resistors, one galvanometer, one variable resistor, and a power source) 2) Ohmmeter Introduction ` Through the use of a Wheatstone bridge setup, we can balance the bridge so that no current will flow through the galvanometer (D to B), and therefore, from Ohm's Law the voltage across the galvanometer must be zero. In addition, the potential difference from C to either D or B must be the same, thus the potential drop across R x equals that of R 2 . Also, the potential difference from A to D and from A to B must be the same. Therefore, = IxRx I2R2 and = I1R1 I3R3 . Then because the current in the galvanometer is zero then the current through R 1 and R x is the same and the current through R 2 and R 3 is the same. Therefore, = IxR1 I2R3 and when the first equation, = IxRx I2R2 is divided by this equation it results that = RxR1 R2R3 . So by measuring the length of R 2 and R 3 (L 2 and L 3 respectively), the ratio of R 2 to R 3 can be determined and R 1 is variable so it can be measured and using these values R x can be calculated. 1
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This note was uploaded on 02/28/2011 for the course PHYS 255b taught by Professor Shoemaker during the Fall '10 term at SIU Carbondale.

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PHYS 255b-004 Lab - Wheatstone Bridge - Wheatstone Bridge...

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